1. Field of the Invention
The present invention relates to a color display device such as a liquid crystal display device or the like, and particularly to improvement in the shape of a color filter pattern having an on-chip color filter structure in which color filters are formed on a driving substrate.
2. Description of the Related Art
There have recently been active developments of a color liquid crystal display using a thin film transistor as a switching element for driving each of pixel electrodes. As such a color liquid crystal display device, for example, the construction shown in FIG. 5 is known. In this conventional example, thin film transistors (abbreviated to "TFTs" hereinafter) for respectively driving pixel electrodes 1 are integrated on a driving circuit 20 made of glass, quartz, or the like. A TFT comprises a channel layer comprising a semiconductor thin film 2, which forms an element region, and a gate electrode 3 formed by patterning through a gate insulating film. The semiconductor thin film 2 has a source region S and a drain region D.
The TFT having the above construction is coated with a first interlayer insulating film 4 on which a signal line-side source electrode 6 is provided by patterning to a predetermined shape. The source electrode 6 is coated with a second interlayer insulating film 5 on which a light shielding film 7 also serving as a pixel electrode-side drain electrode is provided. Each of the pixel electrodes 1 is electrically connected to the drain region D through a contact hole CON formed in the first and second interlayer insulating film 4 and 5.
On the TFTs are formed color filters 8, 9 and 10 for coloring the pixel electrodes 1 to generate the primary colors R, G and B, respectively. Each of the color filters 8, 9 and 10 is segmented and interposed between each of the pixel electrodes 1 and the second interlayer insulating film 5. On the color filters 8, 9 and 10 is formed a planarization film 11 according to demand.
In this way, the color filters 8, 9 and 10 are formed directly on the driving substrate 20 to form a so-called on-chip color filter structure. To the driving substrate 20 is bonded a counter substrate 12 with a predetermined space therebetween. On the inner surface of the counter substrate 12 is formed a counter electrode 13 with a liquid crystal 14 sandwiched between both substrates.
The on-chip color filter structure has various advantages as compared with a structure in which color filters are formed on the counter substrate 12. For example, since the color filters 8, 9 and 10 are overlapped with the pixel electrodes 1, no parallax occurs therebetween, and a high aperture ratio of the pixel region can be obtained. Also, since there is substantially no error in alignment between the pixel electrodes 1 and the color filters 8, 9 and 10, a high aperture ratio can be maintained even if the pixel region is made fine.
FIG. 6 is a schematic plan view of the on-chip color filter structure shown in FIG. 5. The color filter 9 (as an example) shown in FIG. 6 is formed in regions respectively including apertures 16 formed between adjacent light shielding regions 15 and extending to the contact holes CON (refer to FIG. 5) respectively formed between the TFTs and the pixel electrodes 1.
A color filter is generally formed by using a color resist composed of an organic photosensitive material containing a pigment dispersed therein. This color resist contains the pigment dispersed therein and having some particle size, and thus has a problem of resolution, thereby causing difficulties in precisely etching the fine contact holes CON. Namely, the residual color resist remains in the contact holes CON, and possibly causes poor contact.
In order to solve this problem, the inventors developed a method of forming color filters apart from the contact holes CON and disclosed it in Japanese Unexamined Patent Publication No. 8-179376. An example of prior applications is described again with reference to FIG. 7. On the second interlayer insulating film 5 formed as described above are formed the color filters 8, 9 and 10 for the primary colors R, G and B, respectively. Each of the color filters 8, 9 and 10 is segmented and formed apart from the contact holes CON formed in the first and second interlayer insulating films 4 and 5. On the color filters 8, 9 and 10 is formed the planarization film 11 as occasion demands. To the driving substrate 20 is bonded the counter substrate 12 with the predetermined space therebetween. On the inner surface of the counter substrate 12 is formed the counter electrode 13, with the liquid crystal 14 sandwiched between both substrates.
FIG. 8 is a schematic plan view of the on-chip color filter structure shown in FIG. 7. The color filter 9 (as an example) shown in FIG. 8 is formed in alignment with the pixel apertures 16 apart from the contact holes CON. This can eliminates the possibility of poor contact due to the residual color resist in the contact holes CON.
However, in the on-chip color filter structure shown in FIG. 7, since the color filters are formed to be higher than the TFT region, differences in height occur between the color filters and the spaces A between the respective color filters in the example of prior applications in which the spaces A are wide as shown in a plan view of FIG. 8. Namely, unevenness occurs on the surface of the driving substrate, and causes difficulties in achieving sufficient planarization even by providing the planarization film. The occurrence of differences in height on the driving substrate in the sectional direction thereof causes disorder in alignment of the liquid crystal, a reverse tilt domain, or the like, thereby possibly causing deterioration in image quality.